Contact type linear position sensors for measuring the position of members, such as for example, potentiometer based position sensors in which a wiper brushes over the surface of a resistive element, suffer from a variety of drawbacks including a reduced product life, sensitivity to vibration, significant hysteresis and non-linearity, short operating lengths and difficulty in measuring the position of members moving at high speed, such for example high stroke speed pistons.
Non-contact type position sensors are advantageous for making position measurements because position changes of the member can be made without causing wear and tear of the sensor parts unlike contact sensors. However, known non-contact linear positions sensor employed in industrial motion control and other applications for measuring the position of cylinders, pistons, bearings and other members are complex in design and costly to produce. For example the position detection apparatus disclosed in U.S. Pat. No. 5,589,769 entitled “Position Detection apparatus including a circuit for receiving a plurality of output signal values and fitting the output signal values to a curve”, issued to Krahn on Dec. 31, 1996, requires employing an array of magnetic field transducers to sense a magnet position and electronic circuitry to fit the output signals from the transducers to a curve having a cross over point to determine the magnet position. In such position sensors, electronic complexity is dependent on the measuring length. Furthermore, such sensor systems are susceptible to stray magnetic fields and necessitate application of complex algorithms, in the associated signal conditioning circuitry. Additionally, the sensor system requires high power consumption and has a response time which is limited by the sampling of the sensing array for signal conditioning.
There is a continuing need to provide non contact low cost apparatus for effectively measuring the position of a member.
The embodiments disclosed herein therefore directly address the shortcomings of present position sensors providing a low cost apparatus for measuring the linear position of a member that can be integrated more effectively into existing applications.